1. Field of the Invention
This invention is related to a throttle device having a throttle valve.
2. Description of Related Art
In a conventional throttle device which transmits a motor torque to a shaft section of an engine throttle valve by the use of gears, the torque of a motor 101 is transmitted to a shaft 103 of a throttle valve 102 through a gear mechanism as shown in FIG. 5. For example, this type of throttle device has been disclosed by Japanese Patent Laid-Open Nos. Hei 10-89096 and Hei 10-47520. That is, the gear mechanism of such a motor-driven throttle device 100 is comprised of a gear 104 on the motor side mounted on the shaft of the motor 101, an intermediate reduction gear 105 in mesh with the gear 104 on the motor side, and a valve gear 106 mounted on one end portion of the shaft 103 of the throttle valve 102.
The valve gear 106 directly mounted on the shaft 103 of the throttle valve 102 is formed separately from the shaft 103. After fitting its central portion on one end portion of the shaft 103, the valve gear 106 is secured on one end portion of the shaft 103 by tightening a nut 111. The valve gear 106 is provided with an insertion hole 107 at the central section. The shaft 103 of the throttle valve 102 is inserted so that its both end portion will intersect with the intake air passages formed in the throttle body 108, and will be rotatably supported on ball bearings 109.
In the case of a throttle device 100, however, the torque of the motor 101 which has been reduced by the use of the gear 104 on the motor side, a large-diameter gear 112 and a small-diameter gear 113 of the intermediate reduction gear 105, and the valve gear 106, is transmitted to the shaft 103 of the throttle valve 102. However, the valve gear 106 is a component provided separately from the shaft 103, mounted by press-fitting on one end portion of the shaft 103, and furthermore fixed by tightening the nut 111. This type of mounting, therefore, raises such a problem that component count and manhour for installation will increase, resulting in an increased manufacturing cost.
There has been known a throttle device in which the throttle valve 102 and the metal shaft 103 are unitized for the purpose of reducing the component count and manufacturing cost as disclosed for example in Japanese Patent Laid-Open No. Hei 5-141540.
It is, therefore, considered to form the conventional metal shaft 103 and the metal valve gear 106 into a single body. FIGS. 6A, 6B, 7A and 7B show examples for comparison. There is also an idea to manufacture a geared shaft 120 by unitarily molding valve gear 121 and shaft 122 of a resin material. In the geared shaft 120, however, as shown in FIGS. 7A and 7B, the valve gear 121 is different in thickness between axial and radial directions. That is, the valve gear 121 has a non-uniform thickness or an asymmetrical shape. Because of the presence of the thick portion, non-uniform heat shrinkage after resin molding will occur. Consequently, the dimensional change and squareness of the tooth section of the valve gear 121 in relation to the shaft 122 will be deteriorated. In FIG. 7B, the broken line indicates a variation of the gear 121. Therefore it will become impossible to maintain proper engagement of the teeth of the valve gear 121 with the teeth of the intermediate reduction gear 105, possibly resulting in binding, cracking, or other defects of the tooth section of the valve gear 121.
One object of this invention is the provision of a throttle device in which a shaft and a lever for turning the shaft are formed as one body.
Another object of this invention is the provision of a throttle device designed to prevent lever deformation.
Another object of this invention is the provision of a throttle device designed to allow the mounting of a bearing which will be hidden by the lever.
Another object of this invention is the provision of a throttle device designed to allow the mounting of a magnetic sensor.
Another object of this invention is the provision of a throttle device in which the shaft and a gear as the lever are formed in one body.
Still another object of this invention is the provision of a throttle device which enables the reduction of component count and installation man-hours by the unitization of the shaft and the valve gear.
Further another object of this invention is the provision of a throttle device designed to insure proper engagement of the tooth section of the valve gear with the tooth section of the gear on the motor side.
According to one aspect of embodiments of this invention, the valve gear of the geared shaft meshes with the gear on the motor side to transmit the motor torque, thereby controlling the amount of opening of the engine throttle valve by the motor. The use of the geared shaft, in that the shaft and the valve gear are unitized, can decrease a screw fastening component and the number of man-hours. At the same time, a plurality of machining processes which require a high dimensional accuracy can be reduced. Consequently, it is possible to decrease component count, the number of machining processes and installation man-hours, to thereby enable the reduction of manufacturing cost.
The provision of a recess for nearly equalizing the thickness in axial and radial directions in the vicinity of the unitized portion of the valve gear shaft can make approximately uniform a molding shrinkage (called xe2x80x9cshrinkagexe2x80x9d) caused by heat shrinkage of each part of the valve gear. Consequently, a dimensional change in the tooth portion of the valve gear can be controlled, to thereby prevent achieving a right angle and accordingly to maintain good engagement of the tooth portion of the valve gear with that of the gear on the motor side.
According to another aspect of the embodiment of this invention, there is provided a thin-walled section to reduce the weight of the geared shaft. That is, this invention has such an advantage as the reduction of weight and friction loss. As a result, it is possible to use a low-cost motor and to save materials.
According to another further aspect of the embodiment of this invention, through holes are provided at two places or more. Through the through holes, it is possible to insert a press-fitting tool for pressing and fixing an outer ring of a bearing section into the inner periphery of a bearing holding section of the throttle body. Therefore, bearings, such as thrust bearings, ball bearings, etc., can easily be installed in the throttle body by for example press-fitting and fixing. When a ball bearing is used as the bearing section, it is possible to press and fix the inner race on the outer periphery of the shaft and then the outer race into the throttle body. In this case, any play of the ball bearing can be prevented. Consequently, it is possible to prevent valve gear vibration, and accordingly to prevent a valve gear fracture, an increase in engaging torque, and an output deviation of a rotation angle sensor.
According to another further aspect of the embodiment of this invention, the geared shaft has a valve insertion hole unitarily formed, thereby enabling a reduction in the number of machining processes and in manufacturing cost.
According to still yet another further aspect of the embodiment of this invention, the shaft and the valve gear are formed as one body of a non-magnetic material such as aluminum, or stainless steel, etc. Thus it becomes possible to hold components of the rotation angle sensor without giving an adverse effect to the magnetic circuit of the non-contact type rotation angle sensor. The valve gear may be made in the form of, for example, a fan shaped gear. Furthermore, when the shaft and the valve gear are unitarily formed of a metal, the heat of the motor may be transmitted to the geared shaft through the valve gear. Consequently it is possible to use, for instance, a sintered metal which insures effective heat radiation from the motor.